Camping trailers have long been provided with lift mechanisms for raising and lowering the top. Some lifts use telescoping corner posts to accomplish this task.
U.S. Pat. No. 3,363,932 uses a single pumping piston which supplies four separate hydraulic cylinders in four corner posts and has adjustable valves to allow each of the corner posts to descend at an equal rate to the other posts. The valves restrict the flow of fluid returning from the hydraulic cylinders in the corner posts, which adjusts the rate of descent for the cylinder in line with the adjustable valve. If the posts do not descend evenly, binding and excessive wear can occur. In use the weight of the camper top would almost never be evenly distributed to all of the posts. There would almost certainly be some posts which would carry more weight than others. Generally a post with more weight will descend faster than a post with less weight. To compensate for this a user of this disclosed invention would have to adjust each of the four individual valves through trial and error to restrict fluid flow from the individual cylinders in the corner posts until they all descended at the same rate. If a user guessed wrong in his adjustment of one or more of the posts, the camper could bind due to an uneven rate of descent. Also, if the weight distribution changed in any way due to different loading conditions, a user would have to readjust the valves. It is unsafe and unreasonable to expect a consumer to properly adjust the valves each time the camper top is raised or lowered.